European Patent Application Publication Number 0 475 213 Al published 18.03.92 Bulletin 92/12 (hereinafter "EP Application") and U.S. Pat. No. 5,655,282 (hereinafter "USPN '282") disclose a thermal insulating glazing unit having three or more sheets with a spacer frame between and adhered to adjacent glass sheets. This construction of a triple sheet glazed unit has, among other things, the advantage of dead air spaces between adjacent sheets. The dead air spaces eliminate gas movement or gas currents moving between the compartment between the middle sheet and one of the outer sheets (the "first compartment") and the compartment between the middle sheet and the other one of the other sheets (the "second compartment"). In the instance where there is gas movement between the first compartment and the second compartment, the gas in the first compartment is heated or cooled by the outer sheet of the first compartment and moves into the second compartment to heat or cool the other outer glass sheet. This gas movement between the compartments if present reduces the thermal insulating properties of the unit.
Although the design of the multi-sheet insulating unit disclosed in the EP application and USPN '282 has dead gas spaces between adjacent sheets i.e. no gas movement between the compartments, the techniques for making the multi-sheet insulating unit have limitations. More particularly, a spacer frame is provided between adjacent glass sheets requiring the construction of two spacer frames for a unit having three sheets and three spacer frames for a unit having four sheets.
U.S. Pat. No. 5,531,047 (hereinafter "USPN '047") discloses multi-sheet glazing units having one or more inner glass sheets spaced from and between a pair of outer glass sheets. In general, the outer glass sheets are separated by and secured to a spacer frame having a U-shaped cross section. On the base of the spacer frame between the outer legs is a layer of a pliable material having one or more groove(s) for receiving edge portions of the inner glass sheet(s). The unit of USPN '047 is fabricated by positioning a spacer stock around edge portions of the inner sheet(s) while moving the edge portions of the inner sheet(s) into the groove(s) of the pliable material to position the inner sheet(s) within the spacer frame. After the inner sheet(s) is(are) within the spacer frame, the outer sheets are secured to the outer surfaces of the spacer frame by a moisture-impervious sealant. The design of this unit has the advantages of a dead gas space between adjacent sheets and only one spacer frame.
Although the design of the unit disclosed in USPN '047 is acceptable, there are limitations. For example, moving the edge portions of the inner sheet(s) into the pliable material on the base of the spacer stock as the spacer stock is positioned around the inner sheet(s) requires time and precision. More particularly, positioning the spacer stock around the inner sheet(s) may disturb the pliable material on the base of the spacer frame, making the unit unsightly.
U.S. Pat. No. 5,644,894 (hereinafter "USPN '894")discloses multi-sheet glazing units having one or more inner glass sheet(s) mounted within a U-shaped spacer frame and outer sheets adhered to outer surfaces of the spacer frame by a moisture-impervious sealant. The intermediate sheet(s) is(are) held in position by spaced rows of raised portions formed in the base of the spacer frame. The design of these units has the advantage of a dead gas space between adjacent sheets. Although the glazing unit design disclosed in USPN '894 is acceptable, the fabrication of the unit has limitations. More particularly, providing spaced rows of raised portions in the base of the spacer frame requires an extra step in the process of making the spacer frame. Further, mounting the inner sheet(s) between raised portions as the spacer stock is wrapped around the inner sheet requires time and precision.
U.S. Pat. No. 5,553,440 (hereinafter "USPN '440") also discloses multi-sheet glazing units having three or more glass sheets. In general, the units include a pair of outer glass sheets separated by and adhered to outer opposed surfaces of a spacer frame having a U-shaped cross-section. A sheet retaining member mounted between the upright legs of the spacer frame has one or more groove(s) for receiving marginal and peripheral edge portions of one or more inner sheet(s). The glazing units disclosed in USPN '440 are acceptable because the gas movement between the compartments is minimized, if not eliminated; however, the glazing units have limitations. More particularly, positioning the spacer stock around the inner sheet(s) while moving the edge portions of the inner sheet(s) in the groove(s) of the sheet retaining members requires assembly time and precision.
United States Statutory Invention Regulation No. H975 (hereinafter "Publication H975"), published Nov. 5, 1991, discloses a multi-sheet unit having a pair of outer sheets spaced from one another by and secured to a spacer frame. An example of Publication H975 discloses the construction of the unit by mounting edge supports on the edge portions of an inner sheet and setting the inner sheet having the edge supports within the closed spacer frame. Thereafter, the edge supports are secured to the frame. The gas flow between the compartments as discussed in Publication H975 is controlled by the spaced distance between the edges of the inner glass sheet and the spacer frames. Although the design disclosed in Publication H975 is acceptable because gas flow between compartments is minimized, the construction of the unit has limitations. More particularly, mounting edge supports on the edges of an inner sheet and thereafter, securing the edge supports to the spacer frame is time consuming.
As can now be appreciated, it would be advantageous to provide multi-sheet glazing units, i.e. glazing units having three or more glass sheets that have minimal if any gas movement between compartments and do not have the limitations associated with presently available multi-sheet glazing units.